Valve train devices may have an apparatus for switching the lift of gas exchange valves.
A variable valve train is described in US patent specification U.S. Pat. No. 4,354,460, in which a displaceable rocker arm is provided so as to switch between two axially adjacent cams having different cam contours for actuation of the associated gas exchange valve. To this end, a hydraulic unit is provided, with which the rocker arm can be axially displaced on a rocker arm shaft arranged parallel to the camshaft. To this end, a hydraulic piston is provided, to which hydraulic pressure can be applied alternately and which moves a piston rod fastened to the piston. The piston rod is guided within the rocker arm shaft and is connected to the respective rocker arm via recesses. Spring assemblies are arranged on the piston rod and temporarily store the energy for switching the rocker arm until the axial displacement of the rocker arm is released. Each rocker arm of an internal combustion engine is thus displaced axially by means of a plurality of cylinders upon actuation of the hydraulic piston at an accordingly predefined moment in time during encroachment of the base circle overlapping the cams. To actuate the gas exchange valve, a bucket tappet is used, of which the diameter corresponds at least to the displacement path of the rocker arm so that the rocker arm contacts the bucket tappet in each switching position and can thus actuate the gas exchange valve.
Patent specification DE 33 19 755 C2 describes a valve actuation/switching apparatus for an internal combustion engine, in which the two cams, each associated with a gas exchange valve, are partitioned to reduce the necessary switching path of the rocker arm. Each of the two cams is therefore partitioned into two sub-cams. Due to the alternating arrangement of the partitioned cams, the axial displacement of the rocker arm on the rocker arm shaft provided therefor eon be reduced by half of the original cam width. The overall space is thus reduced.